Conventionally, there are various pumps for supplying oil for lubrication and cooling to an engine, each of which includes a relief valve that performs relief in the case where discharge pressure exceeds a predetermined value. In addition, there is also a relief device of an oil circuit of an engine of a type that determines whether or not the relief is executed in accordance with a change in pressure and a change in the temperature of oil.
A specific example of this type includes a third embodiment of PTL 1. The third embodiment of PTL 1 is an oil pump that includes a first control valve (4) and a second control valve (7). PTL 1 will be outlined. Note that reference numerals used in PTL 1 are used without any alterations. The first control valve (4) is configured to function as a relief valve in the case where the discharge pressure of hydraulic oil in a discharge oil path (5) located downstream of an oil pump X is high.
The second control valve (7) is a valve that operates in accordance with the temperature of the hydraulic oil to control the first control valve (4), specifically control the oil pressure of the hydraulic oil that flows into a second valve chamber (44) of the first control valve (4). The second control valve (7) includes a valve body operation mechanism (73) that causes a valve body (72) to reciprocate in accordance with the temperature of the hydraulic oil. The valve body operation mechanism (73) is a temperature-sensitive extendable body (73a) that extends and retracts and, specifically, a spring made of a shape-memory alloy is used as the temperature-sensitive extendable body (73a).
The first control valve (4) and the second control valve (7) are caused to communicate with each other with a first inter-valve oil path (91) and a second inter-valve oil path (92). The control of the oil pressure in a valve body (42) of the first control valve (4) is performed by switching between communication and non-communication with the first inter-valve oil path (91) and the second inter-valve oil path (92). Thus, in PTL 1, the first control valve (4) and the second control valve (7) do not operate independently of each other but operate in cooperation with each other.